The life of a tyre depends inter alia on it being inflated to the correct pressure at all times. Over inflation can cause tread wear and under inflation can cause tyre wall damage as well as tread wear. A device for inflating vehicle tyres is disclosed in U.S. Pat. No. 7,013,931 B2. This device is in an inoperative condition whilst the pressure in the tyre is above a predetermined minimum. More specifically the entire device, apart from a hanging, stationary counterweight, rotates with the vehicle's wheel whilst tyre pressure is above said predetermined minimum. All the parts of the device's pump rotate together in this condition and there is no air pumping action.
Upon a drop in tyre pressure being detected by a sensing and activating structure, a rotating clutch plate is moved axially by a shaft of the sensing device into contact with the stationary clutch plate and it is then prevented from rotating with the remainer of the device.
The pump of the device comprises an eccentric on said shaft and a connecting rod which, at a radially inner end, includes a ring which encircles the eccentric. The outer end of the connecting rod drives a plunger which is within a cylinder and which pumps air when required.
On a low tyre pressure being detected the clutch plate, the shaft and the eccentric cease to rotate. However, the part of the pump comprising the ring, the connecting rod, the plunger and the cylinder continue to rotate. The result is that the ring rotates about the eccentric and the plunger reciprocates in the cylinder pumping air to the tyre. Upon the sensing unit detecting that tyre pressure has reached an acceptable level, the shaft and the clutch plate return to their original position. Relative rotation, and hence the pumping action, cease.
The present invention provides an improved device which allows for both inflation and deflation of the tyre to maintain the correct pressure.